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Topic: Persistent Slabs in the East? (Read 3066 times)

DLottmann

Anyone who's been reading the bulletin's lately will notice we've had a weird snow-pack and been dealing with "Persistent" slabs as well as our typical Wind Slab problems... While things are quieting down (and we have a good storm on the horizon) we got some really interesting results while up in the bowl this past Sunday with an AIARE 1 Avalanche Course. I posted this video of some of the layering we were dealing with and a quick compression test.

With up to 9 inches of snow expected into Wednesday, and a huge storm potential for Sunday, we're about to kick back up to high gear in the ravines. Be sure to check the bulletin daily and "Know Before You Go"!

Dave thats interesting. I know nothing about avalanches but im guessing with the snow we have forceasted there a potential for some big slides, correct? And based off the video, a good sized avalanche could be caused by a relatively low impact force?

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DLottmann

Snow, and avalanches in general, are a very interesting topic in my opinion. While snow avalanches rank very low in comparison to effect on humans when related to other natural disasters (earthquakes, floods, drought, etc) they effect a significant portion of back-country recreationalists, and a lot of research and information is available to those who want to travel in terrain where they occur.

Anytime we get a lot of snow at once you can expect natural avalanche activity. During major storms avalanches will occur; a combination of the amount of precipitation + wind speed & direction = avalanches on certain aspects. Due to the prolonged cold spell we had we had set the stage for potentially deep "delayed action" avalanches, more common in snow climates out west then here in our Maritime snow climate, where avalanche danger tends to drop relatively quickly after storms (a combination of freeze/thaw and generally warmer temps). While there were some crown lines in Tucks and Hillman's Highway we didn't have any major slides on this "persistent" weak layer that has started to stabilize. You could assume this didn't happen for two reasons;

1) Nature didn't tip the balance with additional load during the elevated "danger", i.e. when it was rated "Considerable" and

2) Potential human triggers headed the solid advice from the avalanche bulletin to stay off these touchy areas while things were so unstable.

So to try to answer your two questions... yes, the forecasted amounts of snow most definitely create another natural avalanche cycle, but I don't think they will step down to the deeper layers that have had a chance to start to bond (though I am NOT an avalanche forecaster and will be reading the bulletin's daily before heading into steep terrain). Second, the observations in the video were relevant for that day on that slope... On that day, entering an area with the same buried weaknesses that was steeper, would have made it "likely" for a human triggered avalanche, hence the "Considerable" rating for the day in that area... we were ok on a 32 degree slope with no one above us and no current loading... Had we ventured into a 36-40 degree slope we may have been exposing ourselves more than would be prudent...

Bottom line is to read the bulletin past what the "rating" is for the day. Identify what the problem is... different types of avalanches require different field observations to make, and often different terrain choices... and when in doubt scale back to safer terrain for the day...

In 10 years of learning about avalanches I am always impressed with how much more I can learn...

DLottmann

Nice pic, yup there was also a skiier triggered slide at Jay Peak yesterday and another in the Dackís... Iím waiting on some GoPro footage of the out of bounds Jay Peak one... report is skiier was buried to his chest...